1. Field of the Invention
The present invention relates to a method and an apparatus for producing inorganic spherical particles from inorganic raw material. Particularly, it relates to a method and an apparatus for producing inorganic spherical particles for a sealing material for semiconductors.
2. Discussion of Background
A filler to be used as a sealing material for semiconductors, is required to be free from inclusion of impurities and free from agglomeration or adhesion of particles and to have a stabilized surface condition. Heretofore, as a method for producing inorganic spherical particles such as spherical molten silica to be used as a sealing material for semiconductors, a technique has been proposed, as disclosed for example in JP-A-62-241541 and JP-62-241542, wherein an inorganic spherical powder material is injected together with a gas flame into a spheroidizing chamber and melted and spheroidized, and then rapidly cooled in the connected cooling chamber by a cooling gas blown thereto, to prevent fusion of particles. Namely, in the structure surrounding the flame, circumference of the burner constitutes a spheroidizing zone, and the inner wall is usually constituted by a heat insulating material or refractory. Further, a portion beyond the forward end of the flame constitutes the cooling zone.
However, such a conventional method has problems such that impurities are likely to be included due to damage of the refractory wall in the spheroidizing chamber or due to contact with the refractory wall, and convection of the gas flame is likely to take place in the spheroidizing chamber, whereby a powder is likely to deposit on the inner wall or the upper portion of the furnace, and if the powder deposition grows and the temperature rises, fused ten blocks are likely to form and cause clogging of the burner, scattering of raw material out of the flame, or clogging of the spheroidizing chamber and the cooling chamber, so that the operation can no longer be continued.